P5 Electricity Notes

1.1 What is an Electric Circuit?

An electric circuit is made up of different parts that are connected together to allow current to flow through it.

The different parts of an electric circuit are known as electrical components.

A simple electric circuit consists of:

A battery
Some wires
A bulb
A switch

🔌 A Simple Electric Circuit

1.2 Parts of an Electric Circuit

🔋 Battery — The energy source

A battery is the energy source of an electric circuit.
It has a positive (+ve) terminal and a negative (-ve) terminal.
When the positive terminal is connected to the negative terminal, the chemicals in the battery react to produce energy.

🔌 Wire — The connector

A wire is made of a thin strand of metal.
The most common metal used to make wires is copper.
Wires are used to connect electrical components to one another to allow electric current to flow.
Wires are usually insulated with a plastic/rubber covering.

💡 Bulb — The light source

A bulb is a light source.
A bulb produces light and heat when electric current flows through it.
A bulb is made up of different materials such as glass and metal.

💡 Parts of a Bulb

🔘 Switch — The controller

A switch controls the flow of electric current in an electric circuit.
If the switch is closed, electric current will flow.
If the switch is open, no electric current will flow.

1.3 Closed and Open Circuits

Closed Circuit

A closed circuit is formed when all the electrical components in an electric circuit are connected without any gaps.
Electric current only flows in a closed circuit.
Electric current flows through and lights up the bulbs in a closed circuit.

✅ Closed Circuit — Bulb Lights Up

Open Circuit

An open circuit is formed when there is a gap between the electrical components in an electric circuit.
No electric current flows in an open circuit.
Electric current does not flow through and light up the bulbs in an open circuit.

❌ Open Circuit — Bulb Does NOT Light Up

💡 Key Point: Electric current only flows in a closed circuit. A gap anywhere in the circuit creates an open circuit and stops the flow of current.

1.4 Electrical Conductors and Insulators

Electrical Conductors

Materials that allow electric current to flow through them easily.
Metal conductors: steel, copper, aluminium.
Non-metal conductor: graphite (pencil "lead").

Electrical Insulators

Materials that do not allow electric current to flow through them.
Examples: wood, glass, plastic, rubber.

💡 How to test: Place the object between two crocodile clips in a simple circuit and close the switch. If the bulb lights up → conductor. If it does not light up → insulator.

🧪 Testing Conductors vs Insulators

1.5 Electrical Components and Their Symbols

Component	Symbol	Function
Battery	—\|+ —	Energy source
Wire	——	Connects electrical components to one another
Bulb	⊗	A light source
Switch (closed)	—●●—	Controls the flow of electric current
Switch (open)	—● —●	Stops the flow of electric current

2.1 Changing the Number of Batteries

The larger the number of batteries connected in an electric circuit in series, the larger the amount of electric current flowing through it.
An increase in the number of batteries in series causes an increase in the brightness of the bulb.

⚠️ Warning: If too many batteries are used, too much electric current flows through the bulb and the metal filament will melt/fuse. A gap forms in the filament — the bulb becomes fused and will not light up.

Batteries (in series)	Current	Bulb Brightness
1 battery	Small	Dim
2 batteries	Larger	Brighter
3+ batteries	Even larger	Very bright (risk of fusing!)

2.2 Changing the Number of Bulbs

The larger the number of bulbs connected in an electric circuit in series, the smaller the amount of electric current flowing through it.
An increase in the number of bulbs in series causes a decrease in the brightness of the bulbs.

Bulbs (in series)	Current per bulb	Brightness
1 bulb	Largest	Brightest
2 bulbs	Smaller	Dimmer
3+ bulbs	Even smaller	Very dim

2.3 Light Bulbs in Series vs Parallel

Bulbs in Series

Current flows through each bulb in turn.
There is only one pathway for current to flow.
If one bulb fuses, there is a break in the circuit and the other bulbs will not light up.
As the number of bulbs increases, the brightness of each bulb decreases.

🔗 Bulbs in Series — One Pathway

Bulbs in Parallel

There are separate pathways for current to flow.
The current flows through a different pathway for each bulb.
As the number of bulbs increases, the brightness of each bulb remains the same.

🔀 Bulbs in Parallel — Separate Pathways

Advantages of Parallel Circuits:

Each bulb is brighter than when arranged in series.
When one bulb fuses, the other bulbs remain lit.
Each bulb can be controlled individually using switches.

Disadvantage of Parallel Circuits:

The batteries in the circuit will be drained faster.

2.4 Summary — Series vs Parallel Arrangement

Feature	Series Arrangement	Parallel Arrangement
Brightness when more bulbs added	Each bulb becomes dimmer	Brightness of each bulb remains the same
Current per bulb	Decreases	Remains the same
When one bulb fuses	All bulbs do not light up	Other bulbs remain lit
Controlling bulbs	Bulbs cannot be controlled individually using switches	Bulbs can be controlled individually using switches
Battery life	Batteries will last longer	Batteries will be drained faster

3.1 Conservation of Electricity

Electricity is produced in power stations and passed through underground cables to reach our homes.
Electricity enables electrical appliances to work.
To produce electricity, fossil fuels such as gas, coal and oil are burned in power stations.
Singapore has to spend money to buy fossil fuels — when we waste electricity, we are wasting money.
Burning of fossil fuels is harmful because greenhouse gases and air pollutants are produced.
Air pollutants may cause acid rain; greenhouse gases may cause global warming.
Fossil fuels are limited/finite/non-renewable natural resources.
The more electricity we use, the more fossil fuels we burn — so we should conserve electricity.

💡 How to conserve electricity:

• Use a fan instead of an air conditioner.

• Switch off electrical appliances when not in use.

3.2 Safe Use of Electricity

We must handle electricity with care because it can be very dangerous/hazardous.
Electricity can cause a person to suffer an electric shock and fires to break out.
Lives may be lost and properties destroyed by electric fires.

⚠️ Safety Rules:

• Do not overload a socket by plugging too many appliances into it.

• Do not use a plug or appliance with exposed/damaged/frayed wires.

3.3 Electromagnets

The magnetic strength of an electromagnet depends on:

Amount of current passing through the wire: The greater the amount of current (e.g., by adding more batteries), the greater the magnetic strength.
Number of coils of wire around the rod: The greater the number of coils, the greater the magnetic strength.

💡 How an electric gong works:

1. When the switch is pressed → closed circuit formed → current flows → electromagnets are magnetised

2. Electromagnets attract the iron strip → hammer hits the gong → sound!

3. Metal contact no longer touches the iron strip → open circuit → current stops → electromagnets lose magnetism

4. Iron strip returns to original position → closed circuit again → process repeats rapidly

🔔 How an Electric Gong Works

⚡ Electricity